This invention relates to the preparation of flexible polyurethane foams which are readily anchorable to themselves or some other substance by the application of pressure and heat.
Polyurethanes have been defined as those polymers containing the characteristic urethane linkage, ##STR1## The "urethane polymers" comprise polymers wherein the urethane may be only one of many types of linkages in the polymer chain. Thus, a polyurethane may also be comprised of a wide variety of groups and linkages including oxygen-, sulfur-, nitrogen-, and carbon-containing members such as amino, urea, sulfoamino, amide, acetal, ester, ether and hydrocarbon groups and linkages.
Polyurethanes are prepared by reacting an organic polyfunctional isocyanate with an organic compound having two or more reactive hydrogen atoms (as determined by the well-known Zerewitinoff method) such as hydroxyl or amine groups on polyesters, polyester amides, polyalkylene ethers, polyacetals and polyalkylene thioethers. When a foamed product is desired, water and an excess of isocyanate are added to the mixture. When water reacts with the excess isocyanate groups not previously reacted, carbon dioxide is formed which is entrapped in the reaction mixture. An auxiliary blowing agent, such as a volatile halogenoalkane like a fluorocarbon, can also be employed.
Flexible urethane foams which can readily be anchored thermally, preferably dielectrically, to themselves or to vinyl or other thermoplastic films with a minimum of preparation are of value in a number of applications. The most pertinent reference known to applicant is U.S. Pat. No. 3,244,571, which teaches dielectrically heating the embossing articles formed of dissimilar materials, particularly a supported or unsupported thermoplastic film heat-sealed to a layer of polyester-based polyurethane foam, by introducing impurities in the form of fine particles into the foam formulation in an amount to alter the dielectric properties of the foam to an extent whereby the foam and the thermoplastic film are similarly responsive dielectrically. Polyvinyl chloride, graphite, carbon and iron oxide are recited as suitable impurities. In this system the urethane foam itself fuses with the thermoplastic film. There is no recitation as to the amount of impurity nor as to the criticality of particle size of the impurity.
Although varied formulations and post-treatments of foams have been proposed to accomplish this end, these suffer from the deficiencies of high cost due to extra material and extra handling needed or ineffective sealing under standard sealing conditions. The principal object of this invention is to provide new and improved urethane foam formulations which are readily heat (including dielectrically) anchorable to thermoplastic materials.
Heretofore halogen-containing polymers, including finely-divided solid polymers such as polyvinyl chloride, have been incorporated into flexible polyurethane foams to improve load bearing characteristics of the foams as well as to contribute to flame retardant properties of certain additive combinations in the foams. One such system is shown in U.S. Pat. No. 3,574,149. This reference discloses flexible polyetherurethane foams containing finely-divided halogen-containing resins together with zinc oxide and antimony oxide. While as much as 100 parts by weight of such resins per 100 parts by weight of polyol in the polyurethane formulation can be used "to obtain the desired load bearing characteristics", no more than about 40 parts by weight of such resins per 100 parts of polyol are necessary to achieve the desired flame retardance, and less than 30 parts were employed in the specific examples. Similarly, while the halogen-containing resins can include powder from about 0.0001 to 2 mm., particle size is not critical to the reference system, and the only specific particle size disclosed is 40 microns or 0.04 mm.